The present invention relates to an optical waveguide to be used in an optical thin film component or the like and a manufacturing method thereof. The optical waveguide functions as an isolator for an optical element or as an optical circuit of an optical head to record/reproduce information of an optical disk.
An optical waveguide is the means mainly used to guide light to control much information at high speeds without being adversely influenced by surrounding electromagnetic waves.
An example of a conventional optical waveguide will be described with reference to FIG. 5.
FIG. 5 illustrates the basic structure of a conventional isolator of a model of an optical waveguide.
In FIG. 5, reference numeral 11 designates a monocrystalline substrate formed of LiNbO.sub.3 or the like, 12 a Ti diffusion region, 13 a Ti non-diffusion region, 14 an end part through which light enters, 15 an end part through which light is brought in or out, 16 an end part from which light is projected, and 17 a Y-shaped branching part.
The optical waveguide operates in the following manner.
The Ti diffusion region 12 formed on the LiNbO.sub.3 monocrystalline substrate 11 has a larger refractive index than the non-diffusion region 13. Therefore, light entering from the end part 14 is guided while confined within the Ti diffusion region 12, without spreading to the Ti non-diffusion region 13, and eventually projects from the end part 15. Light entering from the end part 15 is similarly guided to the end part 16 while it is kept confined in the Ti diffusion region 12. At this time, the light is hardly guided to the end part 14 because of optical loss due to the configuration of the Y-shaped branching part 17. This kind of element using LiNbO.sub.3 can serve various functions in an optical device thanks to the acoustooptic effect if an electrode is added thereto.
However, the optical device cannot function unless a semiconductor laser as a light source, a photodetector, and the like are provided as a separate unit from the optical waveguide. Moreover, optical components such as prisms, etc. are necessary to introduce light into or lead light out of the optical waveguide. As such, an alignment technique of considerably high accuracy is required for assembling the prior art optical device.
Since both the optical circuit for introducing light and the optical circuit for detecting light should occupy only a two-dimensional area on the surface of the substrate, it is difficult to make the device compact and lightweight.